Electronic test head positioner for test systems

ABSTRACT

A system for positioning an electronic test head of a test system with respect to an electronic device handler. A positioner assembly moves vertically and provides substantial movement in the horizontal plane with six degrees of freedom. The positioner assembly includes a section for attaching the test head. A counterbalancing assembly is coupled to the positioner assembly to provide a substantially weightless condition to the positioner assembly with the test head attached.

This application is a continuation, of application Ser. No. 522,635,filed Aug. 11, 1983, now U.S. Pat. No. 4,589,815.

Which is a continuation-in-part of application Ser. No. 411,311, filedAug. 25, 1982, now U.S. Pat. No. 4,527,942.

BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention relates to the field of art of electronic test headpositioners.

B. Background Art

In the automatic testing of integrated circuits (IC) and otherelectronic devices, special device handlers have been used which placethe device to be tested in position. The electronic testing itself isprovided by a large and expensive automatic testing system whichincludes a test head which has been required to connect to and dock withthe device handler. In such testing systems, the test head has beenusually very heavy in the order of 75 to 300 pounds. The reason for thisheaviness is that the test head uses high speed electronic timingsignals so that the electronic circuits must be located as close aspossible to the device under test. Accordingly, the test head has beendensely packaged with electronic circuits in order to achieve the highspeed testing of the sophisticated devices.

The prior art has left much to be desired in providing a manipulator orpositioner to easily move the heavy test head accurately into positionwith respect to the device handler mechanism. In some prior positionersthe test head has been positioned by means of lead screws and rotatingand sliding mechanisms each movable one at a time. These prior systemsleft much to be desired in that they did not provide all of the degreesof freedom necessary for easy and accurate docking with the handler. Theuser has had to move the heavy device handler or the heavy positioneritself in order to provide alignment. Other prior art manipulatingsystems have used motors to drive the lead screws in the up/downdirection. Such a motor driven lead screw or even a hand driven oneprovides the possibility of damaging either the test head socketconnections or the connections which are on the device handler due tooverstressing.

Another disadvantage of the prior art systems is that they are large andtake up a considerable amount of floor space which is at a premium intest facilities. A further difficulty of large prior systems hasinvolved the cable which connects the test system to the test head whichis usually short, cumbersome and fragile. Accordingly as a result oftheir size and construction, prior systems could not be movedsufficiently close to the test system.

For purposes of considering patentability, a brief patentability searchwas conducted. The patents identified to be of possible interest in thesearch were:

    ______________________________________                                        Patent No.       Inventor                                                     ______________________________________                                        4,199,294        Streck et al.                                                4,062,455        Carl Flatau                                                  4,132,318        Wang et al.                                                  3,873,148        Robert Kennicuit                                             4,076,131        Dahlstrom et al.                                             4,188,166        Moreau et al.                                                4,273,506        Thomson et al.                                               4,299,529        Inaba et al.                                                 4,264,266        Hans Trechsel                                                3,791,052        Cornelis Van Der Lely                                        3,826,383        Hans Richter                                                 4,303,368        Dent et al.                                                  ______________________________________                                    

Accordingly, an object of the present invention is an electronic testhead positioner that has six degrees of freedom and provides asubstantially weightless condition to the test head which may bemanipulated by hand for easy and accurate docking and undocking of thetest head with the device handler.

Another object of the invention is an electronic test head positionerformed by a column rising vertically from a base which takes little roomon the floor with respect to the test system.

SUMMARY OF THE INVENTION

A system for positioning an electronic test head with respect to anelectronic device handler which comprises a housing including shaftmeans. A positioner assembly has vertical movement along the shaft meansand provides substantial movement in the horizontal plane with sixdegrees of freedom. The positioner assembly includes means for attachingthe test head. Counterbalancing means is coupled to the positioner toprovide a substantially weightless condition to the position assemblywith the test head attached.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are perspective view of a test head positioner system inaccordance with the present invention;

FIG. 4 is an elevational sectional view of FIG. 3;

FIG. 5A is a diagrammatic view of the system of FIGS. 1-3 showing thedocking of a test head with a mechanism plate of a handler;

FIGS. 5B-C is a perspective view and an elevational sectional view ofthe detailed structure of the mechanism plate and test head;

FIG. 6 diagrammatically shows the six degrees of freedom of the systemof FIGS. 1-3;

FIGS. 7A-D show further embodiments of the invention with respect tosecuring the positioner system alongside the test system;

FIG. 8 is a perspective cut away view of a portion of FIG. 3;

FIG. 9 is another embodiment of the present invention in which apressurized cylinder is used;

FIGS. 10 and 11 are perspective views of a further embodiment in whichthe vertical column of FIGS. 1-3 is replaced by a vertical cylindricalsupport tube; and

FIG. 12 is a perspective view of still another embodiment having avertical tube of FIGS. 10,11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 5A, there is shown a test head positioner system10 in accordance with the invention. As shown, positioner system 10carries a test head 11 for a test system for docking with a mechanismplate 17 of an integrated circuit handler 15. It will be understood thatother electronic devices may be handled by device handler such astransistors, chips or dies, etc. In operation, positioner system 10 ismoved manually in a substantially weightless condition to manipulate theheavy test head 11 accurately and precisely and dock it into themechanism plate 17. In docking, location pins 11b are inserted intocorresponding openings in plate 17 and test connector 11a enters andmates with a connector for a device 15a to be tested. The position oftest head 11 may be accurately manipulated in a substantially weightlesscondition to another position with six degrees of freedom substantiallyextensible in the horizontal plane to dock with other mechanism platesin any position. For example, mechanism plates for probers or handlersmay be anywhere from a horizontal plane to a vertical plane.

The details of system 10 are shown in FIGS. 1-3 in which an H-shapedbeam forms a vertical column 12. Column 12 has opposing walls 12a,b witha flange 12c connecting the two walls together. Column 12 is supportedat its bottom by a base assembly 20 having a base plate 22 and outwardlyextending legs 24a-e. Column 12 is secured to plate 22 by bolts 22a forexample. The rear of column 12 is closed by a U-shaped door 14 hinged towall 12b by way of hinges 16.

Test head 11 is supported and manipulated in its docking by a positionerarm assembly 30 which moves vertically on a main shaft 50. Assembly 30comprises a main arm assembly 32, a forearm assembly 34, a wrist jointassembly 36, a cradle assembly 38 and test head adapter plates 40a,b.Main shaft 50 is secured by opposing pillow blocks 52,53.

Positioner arm assembly 30 is counterbalanced to ride vertically on mainshaft 50 by a counter weight assembly 60 having a weight carriage 62which moves vertically in either direction within the rear section ofcolumn 12. Carriage 62 has vertically extending carriage shafts 65a,bsecured thereto and carries removable weights 62a-c. Weights 62a-cexactly counterbalance the weight of assembly 30 and test head 11 sothat they are substantially weightless.

The upper ends of shafts 65a,b threadedly receive members 67a,b swagedto respective ends of cables 68a,b received within grooves of pulleys72a,b of assembly 70. Shaft 74 permits the rotation of pulleys 72a,b andthe shaft is received at an upper end section of column 12. Cables 68a,bextend downwardly along the inner surface of walls 12a,b throughopenings in a plate 230 and are securely fastened by way of swagedmembers to a lift block 80 positioned under main arm assembly 32. Block80 has an opening for receiving shaft 50 and the block slides along web12c and is thus prevented from rotating around shaft 50.

As shown in FIGS. 3, 8, main arm assembly 32 includes an upper bearingblock 86 and a lower bearing block 87 carried by block 80. A main shaftthrust bearing 80a is provided between blocks 80, 87. Blocks 86, 87 haverespective lower extending and upper extending sections 86a, 87a and asshown engage an I beam 90. Specifically, a front wall 90a of I beam 90is secured to front faces of blocks 86, 87 while a rear section 90b of Ibeam 90 is secured to sections 86a, 87a. The vertical and rotationalmovements of assembly 32 may be temporarily locked in any position bymeans of a lock 55 formed in a block 91 as later described in detail. Asleeve 226 concentric with shaft 50 is secured between blocks 87, 91having inner linear bearings 228 which permit the sleeve to travelupwardly and downwardly on shaft 50. Further, sleeve 226 has thrustbearings 227. In this way a unitary main arm assembly 32 is formed whichis adapted to have vertical movement and rotational movement (about avertical axis) on a vertical shaft 50.

To provide velocity sensitive viscous damping for assembly 32, a fluidcylinder 220 has one end fixed to pillow block 52 and the other end toplate 230 secured to the outer surface of sleeve 226. Cylinder 220prevents rapid vertical movement of arm assembly 30 as a safety featurefor operating personnel and to prevent damage to the handler and testhead. Cylinder 220 may be a Bimba model 0920-DP, Bimba ManufacturingCo., Monea, Ill.

Secured to front face 90a are a pair of pillow blocks 95, 96 of forearmassembly 34. A vertical shaft 98 extends through pillow blocks 95, 96.Forearm assembly 34 further includes a forearm 100 having a rear section101 which is bolted to forearm 100 by means of bolts. Shaft 98 extendsthrough vertical opening 107 in section 101 with needle bearings ateither end and a thrust bearing between section 101 and pillow block 96.Forearm assembly 34 may be temporarily fixed in its rotational positionabout a vertical axis by means of a forearm lock assembly 106.

It will be understood that forearm assembly 34 may be effectively turned180° while maintaining all the other elements in their originalpositions. In this manner, rear section 101 extends to the left ascompared to the right as shown in FIG. 3.

Forearm 100 has a front "C" shaped section which rotatively receives anattachment member 120 of wrist joint assembly 36. Member 120 rotateswith respect to forearm 100 by way of vertical upper and lower pivotpins 122. Needle bearings are provided for the rotation of pins 122 inforearm 100 and a thrust bearing 128 is provided between member 120 andforearm 100. Member 120 may be temporarily prevented from rotation withrespect to assembly 34 by means of a wrist joint lock assembly 110 whichis formed within a block 112 secured to the upper surface of forearm100.

Member 120 has a longitudinal opening for receiving a horizontallyextending shaft 300 which is rotated within needle bearings 302 and 304secured to member 120. Shaft 300 at its outer end is welded to aconnecting hub 310 for threadedly receiving cap screws 312 to rigidlysecure back plate 130 of cradle assembly 38.

Cradle assembly 38 is formed by three walls 130-132 welded together toform a U-shaped holder for the test head. Shaft 300 is effective toallow the rotation of assembly 38 about a horizontal axis and assembly38 may be secured in position by tightening of cradle lock assembly 306which is similar to assembly 55.

Walls 131, 132 receive test head adapter plates 40a,b and allow theseplates to rotate with respect to the walls and then to be rigidly fixedin position. Since the structure of both plates 40a,b are the same onlyone of them need be described. Arm 131 has within an end section acircular groove 135 and an opening 136 for receiving a shoulder screw137. A lock knob 140 is threaded into plate 40a and moves about circulargroove 135 in conventional manner. In this way, by tightening lock knob140, plate 40a is rigidly secured with respect to wall 131.

It will now be understood that test head positioner system 10simultaneously positions in six degrees of freedom, X, Y, Z, θ_(X),θ_(Y), θ_(Z). As shown in FIG. 6, it is important for the proper dockingof test head 11 that the test connector 11a have that six degrees offreedom so that it can accurately and effortlessly be positioned withrespect to the device to be tested, 15a for example. If the Y directionwere considered to be the vertical or up/down direction then themovement of assembly 32 vertically with respect to shaft 50 provides theY direction of freedom. θ_(Y) freedom, which is the rotation about the Yaxis is then provided by simultaneous rotation of all of the jointsabout vertical axes 50, 98 and 122.

If the X direction were considered to the left to right direction, thenthat freedom is provided by pivots 50, 98 and 122 in the same manner asθ_(Y). The θ_(X) freedom is provided by shoulder screw pivot 137. Withrespect to Z movement which may be considered to be the in and outmovement, such freedom is provided by pivot shafts 50, 98 and 122 in thesame way as θ_(Y), θ_(Z) is then provided by the pivoting of shaft 300.

Referring now to FIG. 4, there is shown a main arm assembly lock 55which comprises a conventional wedge lock system. Specifically, twowedges 150 and 152 are provided on either side of shaft 50 and arethreadedly engaged by threads 154 of a lock handle 153. By turning lockhandle 153 clockwise, wedge members 150, 152 are brought together andapply pressure onto shaft 50 and this way prevent rotation of block 91about shaft 50 and also prevent a vertical movement of block 91 and theentire assembly 30. Similar lock assemblies are provided for forearmlock assembly 106, wrist joint lock assembly 110 and cradle lockassembly 306 which have turning arms 106a, 110a, 306a respectively.

Referring now to FIGS. 5B,C, there is shown the details of mechanismplate 17 and test head 11. Specifically, mechanism 17 comprises ahandler back plate 17a and a docking gusset assembly 17b. Plate 17acarries a device 15a to be tested which is electrically connectedthrough movable contacts to male connectors 15b fixed to the back planeof plate 17a. Assembly 17b has an opening 200 to allow access toconnectors 15b and effectively provides the back plane with gussets orblocks 202a,b by bolting assembly 17 to the back plane of plate 17a. Itwill be understood that similar gussets may, in a further embodiment, bemounted directly to the back plane.

Each of gussets 202a,b has a centrally located guide opening 204a,b andare adapted to receive guide or location pins 11b of test head 11.Specifically, test head 11 has a docking assembly 205 and testconnectors 11a which are mounted on a test head face plate 206. Guidepins 11b are effective to accurately locate connectors 11a with handlerconnectors 15b.

It will be understood that connectors 11a, 15b are very fragile and mustbe mated with great accuracy to avoid damage. This is particularly aproblem in view of the weight and mass of test head 15. Accordingly,guide pins 11b and blocks 202a,b are effective to keep the connectors11a, 15b separated from each other until the pins 11b are actuallyreceived in guide openings 204a,b which ensures alignment and positiveprecise connection of connectors 11a, 15b. When pins 11b are aligned inthe openings, it is then necessary to pull connectors 11a, 15b together.This is accomplished by means of a cam assembly 210 mounted on plate 206which receives cam follower pins 206a,b which extend outwardly fromblocks 202a,b. Assembly 210 comprises a pair of cylindrical cams 212a,bjournaled at their centers to fixed pivots and which synchronouslyoperate by way of an endless cable 214. Each of the cams has a lowergroove for receiving cable 214 which is tautly coupled between the camsby way of pulleys 214a-d, as shown. Each cam 212a,b has an outwardlyextending handle 215a,b so that rotation of either handles operates bothcams in synchronism with a mechanical advantage of, for example, 5:1.

Each cam 212a,b has a side helical groove 216a,b with an upper cut-outon the upper face for respectively receiving pins 206a,b when pins 11bare in openings 204a,b. Upon turning of one of the handles 215a,b thecams operate in synchronism to pull test head 11 into the plane ofhandler mechanism plate 17, thereby bringing both connectors 11a, 15btogether into mating relationship. After mating, many devices 15a maythen be tested by the handler system. In order to change testconfigurations, it is then necessary to disconnect connectors 11a, 15band then remove the handler from the test head. Accordingly, one of thehandles is operated to pull plate 17a from plate 206 therebydisconnecting connector 11a from 15b.

In this manner, by rotary motion to cam assembly 210 there is producedlinear motion between plates 17a, 206 for the required docking andundocking force.

Each of the guide pins 11b is calibratable and includes an outer pinhousing 203 having an inner chamber which receives a guide pin mount 207having an outer diameter substantially less than the inner diameter ofthe chamber. Mount 207 has an inner chamber for receiving a cap screw209 which extends through an opening which provides substantialclearance. Thus screw 209 may be loosened so that housing 203 may beprecisely aligned on plate 206.

Referring to FIG. 7A there is shown base 22b which is directly boltedonto the floor immediately next to test cabinet 11c of the test system.In still another embodiment shown in FIG. 7B a base 22c has attached toits lower surface along one side a rigid horizontal bar or leg 160.Mounting bolts 162 are used to secure bar 160 to the bottom of cabinet11c. A leveling pad 164 remote from bar 160 provides leveling. A furtherstrut 165 is secured to cabinet 11c and to wall 12a of column 12. Inthis manner, column 12 is secured close to cabinet 11c so that system 10is as close as possible to the test system. In the embodiment of FIG.7C, a base 22d has connected to its lower surface perpendicular legs170, 171 coupled to adjacent sidewalls of test cabinet 11c. A levelingpad 174 is provided. Instead of being bolted to cabinet 11c, bars 170,171 may be extended to the ends of the cabinet as shown in FIG. 7D asbars 170a, 171a. These bars are bolted to each other and also bolted totwo additional bars 173, 175 which secure the remaining two sides of thecabinet. In this way, the four bars 170a, 171a, 173 and 175 are boltedto each other to rigidly engage cabinet 11c to base 22e.

Still another embodiment of the invention is shown in FIG. 9 in whichsystem 250 replaces the weights and cable assembly 60, 68a,b of system10 with a pressurized cylinder 251 having a piston 252. Cylinder 251effectively provides the same function as counterbalance assembly 60 inthat it produces a constant force on arm assembly 30a (including testhead 11) counter to gravity regardless of the actual position of theassembly. The balancing of different weights of assembly 30a may beaccomplished by maintaining a constant pressure within the cylinder 251by means of a regulator 258 supplied by pump 257 and described in detailwith respect to FIGS. 10, 11.

Cylinder 251 is rigidly secured to central web 12c' of column 12 ofFIG. 1. Piston 252 extends upwardly and is fixedly connected to ahorizontal arm 254 which extends through a slot 256 formed in web 12c'.At its other end, arm 254 is fixedly welded to sleeve 226, FIGS. 1, 8.In all other respects, system 250 is substantially similar to system 10.

Referring now to FIGS. 10-11, there is shown a further embodiment inwhich vertical column 12 of system 10 is in system 400 replaced by avertically displaced cylindrical support tube 403. Tube 403 forms acylinder for a piston and telescoping rod 402 with seals 414a,b. As insystems 10 and 250, support tube 403 is supported at its bottom by abase assembly 20b having extending legs 24a-e. Tube 403 and piston 402operate the same as tube 251 and piston 252.

Specifically, a fluid cavity 412 is formed between the piston andcylinder. Fluid under pressure flows into and out of the cavity from afluid source coupled by way of a line 407 through a regulator 404, anpressure gauge 406 to cavity 412. In conventional manner, regulator 404has an opening to atmosphere 404a which allows pressure from cavity 412to be released when it is in excess of the regulator setting 404b. In apreferred example, the fluid is air under a pressure of 25-100 poundsper square inch. This would accommodate a total weight of arm assembly405 including a test head where the test head weighs from 75-300 pounds.In this manner there is achieved a constant pressure "gas spring" sothat positioner arm assembly 405 effectively achieves weightlessness.When it is desired to manually move the position of assembly 405 eitherup or down, the fluid volume in cavity 412 changes which is immediatelycompensated for by pressure regulator 404. Preferably, assembly 405 mayhave a 15-20 inch travel.

Within piston 402 there is disposed a damper 220a having a damper rod222a which is similar to that shown in FIGS. 1 and 8. The top end ofdamper 220a is journaled in a bearing 418 connected to an upper plate424 of arm assembly 405. In this manner, damper 220a is effective todamp the movement of assembly 405 while the rotation of the assemblydoes not adversely twist rod 222a.

Assembly 405 is similar to assembly 30 but has been designed for furthersimplicity. Specifically, rotation and vertical movement of rod 402 maybe locked by a lock assembly 416, as shown. The upper section of piston402 is rigidly secured to mount block 426 to which is secured bearingmount plates 428, 430. Plate 428 has secured to its outer face bearingblocks 428a,b and similarly plate 430 has blocks 430a,b. These blockshave linear bearings for receiving horizontal shafts 432, 434respectively. Locking block 437 secured to plate 428 is effective toreceive shaft 432 and prevent movement thereof when locked. Shafts 432,434 are rigidly connected at their left end to a wrist mounting plate440 which fixedly carries a wrist bearing block 442 having a lockassembly 443 similar to assembly 110. Block 442 has secured to an innersection thereof a wrist joint assembly 36a carrying a cradle assembly38a which are similar to assemblies 36, 38 of system 10.

In operation, as in system 10, all of the locks of positioner system 400are open and then the cradle assembly 38a is moved to its desiredpositioner. That is, assembly 405 may turn about cylinder 403 as well ashorizontally by way of shafts 432, 434 and then to other positionsdetermined by assemblies 442, 36a and 38a. It will be understood thatshafts 432,434, by providing horizontal movement, eliminates the needfor forearm shaft 98 while still providing the above described sixdegrees of freedom. When the desired position is achieved, then therespective locks 416, 437, 443, 306b and the locks of cradle 38a areactuated to maintain the desired position.

A modification of positioner system 400 is shown in FIG. 12 aspositioner system 450. Positioner system 450 is suitable for relativelylightweight test heads since it is a simplified construction having asingle shaft 432a horizontally journaled in blocks 429a,b and 452.Blocks 429a,b and 452 are carried by and secured to a mount block 426awhich is supported by piston 402. The horizontal and rotational movementof the shaft 432a is locked by previously described wedge lock system55a within block 452. Further, the end of shaft 432a is rigidly securedto a wrist bearing block 440a. Block 440a supports a simplified wristjoint assembly 460 which carries cradle assembly 38b. Suitable locks areprovided in blocks 440a, 460 and assembly 38b in the manner previouslydescribed.

What is claimed is:
 1. A system for maintaining an object in asubstantially weightless condition without the effect of gravitycomprising:support means having a first continuously vertical axis;positioner means coupled to the support means and having a verticalmovement with respect to the support means and movement in a horizontalplane, the positioner means including cradle means for attaching theobject; counterbalancing means coupled to the positioner means toprovide a substantially weightless condition to the positioner meanswith the object attached whereby said positioner means is free tomanually move vertically from a predetermined lowermost to apredetermined uppermost position free of mechanical restraints betweenthe two positions; and the positioner means including continuouslyhorizontal linear motion guide means for providing horizontal movementof the object with respect to the support means, the positioner meansincluding a second continuously vertical axis, means for pivotallymounting the object about the second continuously vertical axis, atleast one of said continuously vertical axes being free to rotate as thepositioner means is manually extended, the positioner means having anadditional continuously horizontal axis for providing rotation of theobject about said additional continuously horizontal axis whereby as theobject is extended in the horizontal plane and rotated, the two verticalaxes, the horizontal linear motion guide means, and the additionalhorizontal axis themselves support the weight of the positioner meanswith the cradle means and the attached object without the effect ofgravity.
 2. A system for maintaining an object in a substantiallyweightless condition without the effect of gravity comprising:supportmeans having a first continuously vertical axis; positioner meanscoupled to the support means and having a vertical movement with respectto the support means and movement in a horizontal plane, the positionermeans comprises cradle means including object attachment means, theobject attachment means having pivoting means secured to the cradlemeans for providing rotation of the attachment means about a furtheraxis; counterbalancing means coupled to the positioner means to providea substantially weightless condition to the positioner means with theobject attached; and the positioner means including continuouslyhorizontal linear motion guide means for providing horizontal movementof the object with respect to the support means, the positioner meansincluding a second continuously vertical axis, means for pivotallymounting the object about the second continuously vertical axis, atleast one of said continuously vertical axes being free to rotate as thepositioner means is manually extended, the positioner means having anadditional continuously horizontal axis for providing rotation of theobject about said additional continuously horizontal axis whereby as theobject is extended in the horizontal plane and rotated, the two verticalaxes, the horizontal linear motion guide means, and the additionalhorizontal axis themselves support the weight of the positioner meanswith the cradle means and the attached object without the effect ofgravity.
 3. The system of claims 1 or 2 in which the positioner meansincludes additional means for mounting said positioner means on thesupport means, and means for rigidly connecting said additional mountingmeans to prevent relative vertical movement between said cradle meansand the additional mounting means.
 4. The system of claims 1 or 2 inwhich both the continuously horizontal guide means and the additionalcontinuously horizontal axis are free of vertical movement with respectto each other.
 5. The system of claims 1 or 2 in which at least thesecond continuously vertical axis, the horizontal guide means and theadditional horizontal axis are all free of vertical movement amongthemselves.
 6. The system of claims 1 or 2 in which positioner meansincludes means for mounting the positioner means on the support meansand in which the second continuously vertical axis, the horizontal guidemeans and the additional horizontal axis are all free of verticalmovement with respect to the mounting means.
 7. The system of claims 1or 2 in which the guide means includes means for providing onlyhorizontal movement of the cradle means with respect to the supportmeans.
 8. The system of claim 3 in which said additional mounting meansmounts said positioner means for sliding movement of the positionermeans with respect to the support means.
 9. The system of claim 3 inwhich the horizontal linear motion guide means includes two continuouslyhorizontal members for providing the horizontal movement.
 10. The systemof claim 9 in which the second vertical axis, the horizontal linearmotion guide means and the additional horizontal rotational axes arefree of vertical movement with respect to the cradle means.
 11. Thesystem of claim 2 in which said positioner means is free to manuallymove vertically form a predetermind lowermost to a predetermineduppermost position free of mechanical restraints between the twopositions.
 12. The system of claims 1 or 2 in which saidcounterbalancing means includes a fluid cylinder and piston rod, one ofwhich is rigidly fixed to the support means and the other supports thepositioner assembly, means for setting the fluid pressure in the fluidcylinder to a predetermined value and for maintaining that valuesubstantially constant for all vertical positions of the positionermeans.
 13. The system of claim 12 in which the support means includesvelocity sensitive means for providing viscous damping for thepositioner means.
 14. The system of claim 1 in which said cradle meansincludes object attachment means having pivoting means secured to thecradle means for providing rotation of the attachment means about afurther axis.